Terference printed board and similar transmission line structure for reducing in

ABSTRACT

A novel transmission-line structure, particularly adapted for printed circuit sheets and the like, and embodying zig-zag line conductors formed of conductive strips successively disposed on opposite sides of the insulating sheet and interconnected transversely through the sheet, with the corresponding strips of each line conductor crossing those of the other line conductor, through on opposite sides of said sheet, effectively to provide a twist of the line conductors through at least a turn to effect magnetic field cancellation, self-shielding and interference suppression.

ilnited States Patent 1 1 Schlessel 1451 Sept. 4, 1973 1 1 PRINTED-BOARDAND SIMILAR TRANSMISSION-LINE STRUCTURE FOR REDUCING INTERFERENE [76]Inventor: Joseph Schlessel, 7A Sycamore Dr.,

Great Neck, NY. 11021 [22] Filed: Sept. 18, I972 121 App]. No.1 289,871

[52] US. Cl 174/33, 174/34, 174/68.5, 174/117 FF, 333/99 R [51] Int. ClH011) 11/02, 1101b 7/08 [58] Field of Search 174/32, 33, 34, 117 R,174/117 F, 117 FF, 68.5; 333/99 R, 81 A, 73 S 156] References CitedUNITED STATES PATENTS 2,754,484 7/1956 Adams 174/33 X 3,091,655 5/1963Ruiter 174/32 3,033,970 5/1962 Eisler 174/117 FF X 2,857,450 10/1958Oliver 174/34 3,587,169 6/1971 Bcnke et al...... 174/34 X 1,792,2732/1931 Byk et a1 174/34 Primary Examiner-Bernard A. Gilheany AssistantExaminerA. T. Grimley Att0rneyRines & Rines [5 7] ABSTRACT A noveltransmission-line structure, particularly adapted for printed circuitsheets and the like, and embodying zig-zag line conductors formed ofconductive strips successively disposed on opposite sides of theinsulating sheet and interconnected transversely through the sheet, withthe corresponding strips of each line conductor crossing those of theother line conductor, through on opposite sides of said sheet,effectively to provide a twist of the line conductors through at least aturn to efiect magnetic field cancellation, selfshielding andinterference suppression.

4 Claims, 5 Drawing Figures PRINTED-BOARD AND SIMILAR TRANSMISSION-LINESTRUCTURE FOR REDUCING INTERFERENCE The present invention relates totransmission-line structures for printed boards and the like, being moreparticularly directed to structures designed for reducingelectromagnetic interference in electronic and other equipment employingprinted, etched or other wiring, secured upon insulating surfaces byautomatic printing, etching, stamping or other methods.

In conventional hand-wired electronic equipments, shielding of criticaltransmission paths has conventionally been performed in a number ofways. If electromagnetic waveguides are employed, forexample, containingelectromagnetic energy within them, interference from outside sourcesentering the guides is completely prevented by the guide walls. Coaxialcables have also been used to conduct signal energy along a centralconductor which is shielded from outside influences by an outer metallicsheath, constructed in a variety of ways, and which is also used as areturn conductor. If a lesser degree of shielding from outsideinfluences is tolerable, other transmission lines, including twistedpairs of wires, have been used; wherein magnetic fields impinging onsuch pairs of wires induce pposing voltages in different portions of thetwisted pair. Since these portions are adjacent to one other and repeatat regular alternate intervals, fairly effective shielding againstelectromagnetic intereference has been thus obtained.

Since all of the above transmission-line structures, however, haveembodied the use of separate wires and cables connected between each ofthe sources and loads, their use to reduce interference effects inprinted wiring circuits and the like has generally not been attemptedfor several reasons. First, the conductor pattern on a printed circuitboard can only be applied to oneor both of the two surfaces of theinsulating board material, with the conductors applied as a single orfewlayered surface deposit. Secondly, if two-sided printed circuits areused, the connections between the two sides have been deliberatelyrestricted to as few as possible, the boards being typically soldered onthe bottom surface only, using a dipping process or an automatic machinehaving a solder wave. Reliable connections to the top of the board,indeed, are achievable, in practice, only by additional manual solderingto the top (or component side) of the printed circuit board.Consequently, multi-conductor circuits having minimal radiationcharacteristics have not heretofore been considered as feasible in thesetypes of constructions.

Instead, other shielding approaches have been proposed, includingmultiple layer and conductor constructions for reducing interference inprinted board circuits as described, for example, in U.S. Letters PatentNo. 3,460,105; actual ground and interposed insulating strips andshields as described, for example, in U.S. Letters Patent No. 2,754,484;and multi-parallelconductor laminates, as described, for example, inU.S. Letters Patent No. 3,118,016. Such proposals, however,disadvantageously all require extra or ancillary layers and/orconductors and are not thus adapted for ordinary single printed boarduse and the like.

In accordance with a discovery underlying the present invention,however, it has been found that a novel zig-zag, alternatingopposite-side conduction strip transmission line can be provided uponeven single insulating boards and the like so as inherently to reduceradiation interference along the line.

An object of the present invention, accordingly, is to provide a novelconductor printed circuit transmission line structure that produces andis minimally sensitive to electromagnetic and electrostatic radiation.

A further object of the invention is to provide a novel printed circuittransmission line somewhat analagous to a twisted or braided conductorpattern in performance. Still a further object is to provide a noveltransmission line or more general utility, as well, and having minimalmutual interference characteristics.

Other and further objects are later described, being 'more fully pointedout in the appended claims. In summary, however, from one of its broadaspects, the invention contemplates a transmission line structurecarried by an insulating sheet, having, in combination with the saidsheet, a pair of zig-zag transmission line conductors each comprising aplurality of conductive strips successively disposed on opposite sidesof said sheet and interconnected by conductive means extendingtransversely through said sheet; input and output terminal meanscorrespondingly provided at the strips at opposite ends of the lineconductors; and the line conductors being disposed such that thecorresponding strips of each line conductor cross those of the otherline conductor, though on opposite sides of said sheet, effectively toprovide a twist of the transmission line conductors though at least aturn to effect magnetic field cancellation, self-shielding, andinterference suppression.

The invention will now be described with reference to the accompanyingdrawings,

FIG. 1 of which is a top view of a two-conductor transmission lineconstructed in accordance with a preferred embodiment of the invention;

FIG. 2 is an isometric view, upon an enlarged scale of part of the lineof FIG. 1; and

FIGS. 3, 4 and 5 are schematic views similar to FIG. 1 of modificationsof the conductor patterns.

Referring to FIGS. 1 and 2, a source S of electric sig nals is shown atinput terminals 1' and 35 connected, respectively to first conductorstrips 1 and 35 disposed on the top surface of a supporting insulatingsheet I. Each of the conductor strips 1 and 35 is the first of aplurality of strips (59-l317 and 31-27-23-19) respectively comprisingsubstantially equal-length segments of such a pair of transmissionlines. The current passing through each conductor strip'(such as thestrip 1) is fed transversely through the sheet I to the next successivestrip (5) by through-connectors (3). Such through-connectors'as 3, 7,11, etc., may take various forms, such as a metallic insert of rolled orseamless eyeletform, wire, or a plated connection, such as aplated-through hole. Successive strips l-5-9l3-l7 (and 35-3l-27-2319)are disposed on opposite sides of the insulating sheet I and arranged inzig-zag fashion such that corresponding strips of each line (5 and 35, 9and 31, 13 and 27, and 17 and 23) cross one another, but insulatingly,on opposite sides of the sheet 1. Connections transversely betweenopposite sides of the printed circuit board, as at 3, can be reliablyaccomplished by plating conductive material (such as copper) on theinside wall of holes drilled or punched through the printed circuitboard, as at 3, can be reliably accomplished by plating conductivematerial (such'as copper) on the inside wall of holes drilled or punchedthrough the printed circuit board, permitting a multitude of reliableconnections to be made from one side of the printed circuit board to theother and thereby obviating the need for soldering manually allconnections to the top of the printed circuit board. Suchthrough-connections can thus be used as a useful interconnecting ofcircuit elements, rather than as an undesirable and to-be-avoidedconnection, as in the prior art.

Tracing the current from the source S, after passing through transversethrough-connector 3, the current from the left-hand terminal of source Sis next passed along bottom surface conductor 5. The current is thenconducted via through-connector 7 to top surface conductor 9; then bythrough-connector 11, to bottom surface conductor 13; bythrough-connector 15, to top surface conductor 17, etc.; and ultimatelyto the lefthand terminal of load resistance L, which may be any desiredutilization means.

Current from the right-hand terminal of load resistance L is returned tothe right-hand terminal of source S via top surface conductor 19,through-connector 21 bottom surface conductor 23, through-connector 25,top surface conductor 27, through-connector 29, bottom surface conductor31, through-connector 33, and top surface conductor 35, FIG. 2.

In essence, the energy from source S is thus conducted to load L via apair of conductors which have experienced a right-hand zig-zag twist oftwo complete turns, although the actual conductor portions are locatedon the flat surfaces of insulating medium I and in transverse electricconnections passing through the board medium I.

An electric current passed from source S to load L would normallygenerate a magnetic field perpendicular to the plane of insulator boardI, this field being proportional to the product of the current and thearea II formed by the portions of, for example, conductors 5, 9, 31, and35 enclosing it. If the structure described above were constructedsymmetrically, a magnetic field of the same magnitude, but oppositepolarity, would be created by the same current in area III formed by theportions of conductors 9, 13, 27, and 31 enclosing it. These twoopposing magnetic fields would cancel each other at a distance largecompared to the dimension of a full twist, and show a substantialreduction in field strength (compared to the field of a single area) atcloser distances. In essence, the effective twisting of the conductorshas shielded the transmission line.

The same analysis can be made and the same result can be achieved forfields in the left-right direction. Here, the product of length of theconductor portions and the thickness of the insulating medium I form therelative areas.

By reciprocity, the strength of the induced voltage due to an externalalternating magnetic field is proportional to the magnetic fieldgenerated by the conducted current. Consequently, such a transmissionline shows little susceptibility to interference from external fields.

Heretofore, transmission lines of printed circuit construction have beenrestricted to those configurations which did not involve crossing ofconductors via connections through the insulating medium and werepractically restricted to parallel conductor construction. In suchcases, interference reduction could only be accomplished by having theconductors as narrow as possible and the insulating medium as thin aspossible. It

can readily be appreciated that this prior-art construction is severlylimited in both physical strength and the transmission linespower-handling capability, while demanding high precision in itsconstruction.

The present invention, aside from being quite noncritical as tothickness or strength of insulating medium or conductor thickness, isalso very tolerant of any misalignment between the top-surface and thebottomsurface conductors. This may be seen by imagining thebottom-surface conductors all being displaced to one side. The size ofthe areas II and III would not be changed, though thethrough-connections would no longer fall on the center of the bottomconductors.

The conductor construction of FIGS. 1 and 2 is illustrated for atransmission line of relatively low capacitance. If a lower impedance isdesired, this can be achieved by having a higher proportion of theconductors located on top of each other. This is schematicallyrepresented in FIG. 3 where the solid lines indicate topsurfaceconductors, dashed lines indicate bottomsurface conductors, and dotsrepresent the throughconnections. The conductor segments here havestraight intermedate sections between oppositely extending crossingportions, forming somewhat Z-shape conductor segments.

In applications where a multitude of transmission lines must operate inclose proximity, each carrying different signals and being susceptibleto interference from signals in the other transmission lines, aconstruction may be effected in accordance with the invention in whicheach transmission line is twisted or transposed at a different pitchcompared to its neighbors. This is shown schematically in FIG. 4, withthe same symbol notations as FIG. 3. Here, four transmission lines areschematically shown, with the first or left-hand transmission lineexperiencing three complete turns; the second, two complete turns; thethird, one and one-half turns; and the fourth, one turn in the lengthshown. This type of zig-zag construction may be made to any desiredlength and with any number of conductors, limited only by thefabrication facilities.

In certain applications, moreover, it is sometimes desired to havetransmission lines of more than two conductors. The present inventionreadily allows twisting of any multiple number of conductors, asschematically shown in FIG. 5 for the case of a four-conductortransmission line cable. Conductors A, B, C, and D are twisted abouteach other for one full turn, while auxiliary conductors E and F,carrying non-critical currents, have been allowed to pass between thetop spaces between the conductors. The lengths of the conductor segmentsin this embodiment may thus be different for the successive segments.

The technique described above is not, however, restricted to twistedmultiple conductors, but may with equal ease be applied to conductorconfigurations of a braided or woven shape, now possible only withindividual wire conductors. Similarly, the invention is not restrictedto rigid printed circuit applications, but may be used with flexible,thin insulating films as well. The invention, furthermore, is notrestricted to conductors and through-connectors made by conventionaletching and plating methods, but is usable with constructions made byother suitable processes, including those involving diffusion processesor vacuum deposition processes. Further modifications will also occur tothose skilled in the art, and all such are considered to fall within thespirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. A transmission line structure carried by an insulating sheet, havingin combination with the said sheet, a pair of zig-zag transmission lineconductors each comprising a plurality of conductive strips successivelydisposed on opposite sides of said sheet and interconnected byconductive means extending transversely through said sheet; input andoutput terminal means correspondingly provided at the strips at oppositeends of the line conductors; and the line conductors being disposed suchthat the corresponding strips of each line conductor cross those of theother line conductor, though on opposite sides of said sheet,effectively to conductive strips of a plurality of different lengths.

IF l l

1. A transmission line structure carried by an insulating sheet, havingin combination with the said sheet, a pair of zig-zag transmission lineconductors each comprising a plurality of conductive strips successivelydisposed on opposite sides of said sheet and interconnected byconductive means extending transversely through said sheet; input andoutput terminal means correspondingly provided at the strips at oppositeends of the line conductors; and the line conductors being disposed suchthat the corresponding strips of each line conductor cross those of theother line conductor, though on opposite sides of said sheet,effectively to provide a twist of thE transmission line conductorsthrough at least a turn to effect magnetic field cancellation,self-shielding, and interference suppression.
 2. A transmission-linestructure as claimed in claim 1 and in which said zig-zag configurationcomprises a plurality of substantially equal-length successiveconductive strips.
 3. A transmission-line structure as claimed in claim1 and in which said zig-zag configuration comprises conductive stripseach of substantially Z-shape.
 4. A transmission-line structure asclaimed in claim 1 and in which said zig-zag configuration comprisesconductive strips of a plurality of different lengths.